E. T. DUMBLE-THE SOILS OF TEXAS. 
29 
principally, of granitic materials, sandstones or limestone, and the few 
clays which were deposited were metamorphosed into slates. 
With the beginning of the Carboniferous, however, the clays appear 
as the equals at least of the sand and lime, even if they be not in excess 
of either of them. 
Very early in this period a great fold was formed, the ridge of which 
extended northward from the Central region to Indian Territory, and in 
the basin thereby created to the west of the ridge were deposited the 
greater portion of the beds of the Coal Measures. These beds in the east¬ 
ern portion, or Central Coal Field as we know it, are of clay, lime and 
sand, and were largely derived from the rocks of the Llano region and 
from Indian Territory. The southern shore line of this Carboniferous 
sea, with its numerous bays and headlands, is plainly traceable through 
Lampasas and San Saba counties to-day. In the west, beyond the Pecos, 
the sea was deeper and conditions different, so that by far the greater 
part of the deposits are limestones. 
As the Coal period gave way to the Permian, the sea which covered 
what is now the northwestern part of the State became gradually shal¬ 
lower, with corresponding changes of conditions of deposition, and we 
have the clays and clayey limestones of the early Permian, followed by 
sandy clays and sands, with the great beds of "salt and gypsum which 
mark the closing of that period and with it the close of the Paleozoic era. 
The sandy beds of the Triassic, which ushered in the Mesozoic, are 
now exposed only as a fringe around the eastern and northern border of 
the Llano Estacado. Their original extent is unknown, but it is proba¬ 
ble that they covered a large area east of their present boundaries, and 
that it was largely from this source that the basal sands of the succeed¬ 
ing deposits were derived. 
Following the Triassic, so far as our present evidence shows, there was 
a long period in which dry land prevailed over the entire State, and in 
consequence no deposits were formed. 
This was followed by the incursion of the Lower Cretaceous sea from 
the south and west. The waters gradually crept inland until they cov¬ 
ered almost if not the entire State east of the Pecos, except the Central 
Mineral Region, which appears to have been uncovered up to the close 
of the Fredericksburg period at least. If later deposits covered it, there 
now remains no direct evidence of the fact. In Trans-Pecos Texas, the 
waters of this sea seem not to have covered the mountain blocks of El 
Paso county, but to have met in them barriers to their progress, and in 
consequence the deposits of this period are mostly found in the valleys 
or flats. In this region the deposits of the latter part of the Lower 
Cretaceous are much thicker than are those of the eastern part of the 
State, 
